src/threads/thread.c

@@ -391,6 +391,15 @@ thread_set_priority (int new_priority)
 
   enum intr_level old_level = intr_disable ();
 
+  /* If the thread is in the ready list, the list must be reordered to maintain
+    the priority order. */
+  if (thread_current ()->status == THREAD_READY) {
+    /* Remove from the ready list and reinsert it in priority order. */
+    list_remove (&thread_current ()->elem);
+    list_insert_ordered (&ready_list, &thread_current ()->elem, priority_more,
+                         NULL);
+  }
+
   if (new_priority < old_priority && !list_empty (&ready_list)) {
     /* If the new priority is lower than the old priority, check if the current
        thread no longer has the highest priority. If it doesn't, yield the CPU.